This invention relates to filter assemblies for trapping pollutants which may be present in a fluid flow and more particularly to filter assemblies of the kind having a porous filter element supplemented by screening means and having a by-pass valve for transmitting fluid independently of the filter element in the event that the filter becomes clogged.
Filter assemblies are used in various fluid systems to remove foreign particles, such as dirt, metal chips and the like, which may be present in a fluid flow. For example, tractors and earth-moving vehicles often have fluid cylinders or motors operated by hydraulic fluid which is pressurized by a pump driven by the vehicle engine. The hydraulic fluid, which may typically be oil, is drawn from a tank carried on the vehicle and returns to the tank after discharge from a motor or other hydraulic device. A filter assembly is usually provided to entrap solid particles such as dirt, metal slivers and the like which can otherwise accumulate in the tank and disrupt or damage the operation of fluid circuit components. Filter assemblies may also be desirable in other flow systems such as the fuel lines or lubricating oil system of a vehicle and also in non-vehicular apparatus of various kinds known to the art.
A common type of filter assembly utilizes a cylindrically shaped replaceable porous filter element typically formed of paper or other cellulosic material and also has a fine mesh screen for entrapping larger solid matter. It is possible for the filter element to become sufficiently clogged to inhibit fluid flow and this can cause a variety of undesirable effects including a pressure buildup at the intake side of the filter assembly. To avoid the serious consequences of flow blockage, by-pass valves have sometimes been provided which respond to a predetermined pressure buildup at the input to the filter assembly by enabling fluid to return directly to the tank without passing through the filter.
It has heretofore been the common practice to situate the cylindrical screen and filter element in close coaxial relationship to each other in an arrangement where the flow to be filtered normally passes radially inwardly or outwardly through the combined screen and filter element. It has also been a common practice to situate the by-pass valve in an arrangement where by-pass fluid is not only returned directly to the tank without any cleansing action whatsoever, but also must necessarily pass along the contaminated side of the screen and filter combination in order to reach the tank.
In prior art systems of the kind discussed above, it is not possible to replace, clean, or service the screen or the filter element without disturbing and manipulating both elements. This not only complicates maintenance but tends to cause the release of entrapped contaminants back into the flow system. Further, the by-pass arrangements may result in fluid being returned to the tank with no cleansing action whatsoever and under conditions where material previously entrapped on the filter tends to be released back into the fluid flow.
Typical prior filter assemblies are disclosed in prior U.S. Pat. Nos. 3,572,508; 3,358,835; 3,000,505; 3,221,888; 2,743,019; 2,743,017; 2,076,935 and 2,057,219. In each instance, the filter assemblies of these prior patents display one or more of the structural characteristics discussed above.